We propose to continue the study of the biological and physico-chemical properties of the isolated LDL receptors, using receptors labeled either biologically or chemically with appropriate radioactive precursors or reagents. An important part of these studies is the development of more precise methods for the quantitation of the isolated LDL receptors, since such methods would assist in the purifications of the receptors. Once sufficiently purified preparations of the LDL receptors are available, we will undertake the preparation of specific antibodies. These will be used to study the distribution of LDL receptors on the surface of a variety of cells or tissues. We propose to study the physico-chemical parameters of chondroitin-6-sulfate (such as molecular size, degree of sulfation, requirement for free carboxylic groups) which are necessary for its interaction with LDL. We will continue the study of the metabolism of cell surface glycosaminoglycans in human mutant fibroblasts "receptor-negative" for the LDL receptors.